The proposed research will apply methods from synthetic and physical inorganic chemistry to selected transition metal proteins and enzymes possessing unusual structural features, as evidenced by their spectroscopic and catalytic properties. The general objective of the research is to understand how the chemical environment of the metal ions leads to their distinctive spectroscopic and catalytic properties. This will be accomplished by fundamental physical and chemical studies of an unusual iron-containing hydrolytic enzyme, and by the preparation of synthetic models for the interaction of iron-sulfur clusters with other chromophores in certain complex iron-sulfur enzymes. The specific examples to be investigated in this research are two biologically significant iron-containing systems: the purple phosphatases, and iron-sulfur enzymes with flavin or heme prosthetic groups. The purple acid phosphatase from bovine spleen contains a novel spin-coupled binuclear unit at or near the active site. Spectroscopic and chemical methods will be employed to determine the nature of this unusual prosthetic group in the bovine and other similar enzymes, and the role of the prosthetic group in catalysis of a simple hydrolytic (rather than an oxidation-reduction) reaction. Iron-sulfur clusters containing covalently bound flavin or porphyrin groups as ligands will be prepared and characterized, in order to allow an examination of the factors affecting electron transfer and magnetic interactions between these redox active groups. Many enzymes, as well as components of the mitochondrial electron transport chain, are known to contain and to transfer electrons between similar units.